Apollo 17 – NASA, 1972. Geologist-Astronaut Harrison Schmitt worked next to a huge, split boulder at geology Station 6 on the sloping base of North Massif during the third Apollo 17 extravehicular activity. Artist NASA. (Photo by Heritage Space/Heritage Images via Getty Images)
Heritage Space/Heritage Images via Getty Images
Of our Moon’s many remaining secrets, one could be evidence for Earth’s earliest biology in what has been termed a lunar ‘lava sandwich.’
Finding organics beneath ancient lunar lava, oddly enough, has the potential to usher in a game-changing understanding of life’s origin on Earth. Our own planet’s active geology squelched our ability to retain a full history of the onset of life. But the Moon’s geological record may open a window in time that eludes us here on Earth.
Records of organic and biological evolution on Earth stopped around 3.8 billion years ago, Mark Sephton, a geochemist at the Royal School of Mines at Imperial College London, tells me in his office. Yet, the Moon may contain older preserved materials that were circulating near to Earth when it was just becoming habitable, Sephton tells me.
First there would need to be a lava flow from the lunar interior that acts as a bit of lunar asphalt on which an organically, or potentially bio-rich meteorite or planetary fragment would serendipitously fall onto the lunar surface. Then within a relatively short geological time frame — perhaps spanning as little as only tens of millions of years, a second lunar lava flow or eruption would insulate the organic material in a protective ‘lava sandwich.’
It could literally be almost any spot on the Moon that underwent a lava repaving, says Sephton. The only caveat is that you would have to have some delivery mechanism to the surface of the nascent Moon, so that this meteoritic or planetary material would arrive when the first layer of lava was already down, he says.
In theory, as Sephton and colleagues noted in a 2015 study, such a lava sandwich could protect this precious trapped material from cosmic ray exposure and/or further degradation for billions of years.
In other words, such materials may simply be waiting for future robotic probes to find them — potentially either in exposed lunar outcrops or by drilling beneath the surface itself.
We often talk about the transition from prebiotic to biotic, says Sephton. There is little evidence of this on Earth because of the rock cycle, he notes. But perhaps records of the first chemical steps towards life were ejected into space and then fell onto the Moon, says Sephton.
In a 2002 paper appearing in the journal ICARUS, the authors note that our Moon may preserve material not only from Earth, but also from Venus. The only attainable record of Venus’ early surface geology, catastrophically erased 700 million years ago, is probably also on the Moon, they write.
It’d be interesting to see molecules where early life has started to generate molecular machinery that’s working but isn’t quite as efficient as the molecular machinery that we have in our present-day biosphere, says Sephton.
Are any regions of the Moon particularly good candidates for such samples?
There are multiple places on the Moon with layered lava flows, Oceanus Procellarum — a large near-side lunar mare — is certainly one, as are other mare regions, Ian Crawford, a planetary scientist at the University of London’s Birkbeck College, tells me via email.
High-resolution imaging from NASA’s Lunar Reconnaissance Orbiter has also identified many potential localities where layering is exposed in the walls of rilles, craters and collapse pits, he says.
As for taking an actual sample?
We would take the samples and liberate organic compounds either by extracting them with organic solvents or by heating (thermal extraction), says Sephton. The latter requires flash heating the sample to fragment the molecules, he says.
Although it would be cheaper for a potential lava sandwich prospecting mission to perform its own analysis in situ, ideally, such bio-interesting organic samples would best be returned to Earth-based labs.
Bringing samples back is the best; we’re still benefiting from the rocks that came back from the Moon, says Sephton. The longer these samples are on Earth, the more opportunity for people to come along and say, “I have a new technique; a new type of mineral characterization; a new question,” he says.
The Oceanus Procellarum on the lunar Near Side as taken by NASA’s Lunar Reconnaissance Orbiter Camera (LROC).
NASA/Goddard Space Flight Center/Arizona State University
Ancient Lava
The oldest lava flows will be buried by younger ones so identifying and sampling these may mean drilling down hundreds of meters, which will require quite a lot of infrastructure, so a Moon base would help, says Crawford. But there are other options for paleoregolith preservation in addition to lava flows, he says.
Case in point, in 1972, Apollo 17 astronaut Harrison ‘Jack’ Schmitt, the only geologist to walk the lunar surface, stumbled across orange and black pyroclastic beads in the Moon’s Taurus Littrow Valley. These kinds of pyroclastic volcanic eruptions could have conceivably cloaked and preserved ancient organics as well.
The ideal case would be to find a terrestrial meteorite containing organic molecules, or conceivably micro-fossils, from a time that Earth’s own geological record has not preserved, says Crawford.
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